pkg/instance: support injected boot for vmm
pkg/instance: support injected boot for vmm

If pkg/build produces a kernel, inject it into vmm config too.
This will allow continuous build with vmm VM type.

Update #712

xairy/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller